- A
Replace subprocess with os.system()
Why wrong: os.system() also uses a shell and is even less secure than subprocess with shell=True.
- B
Use the 'shlex.quote()' function to sanitize user input before passing to subprocess
Why wrong: While sanitization helps, it is still prone to bypasses and does not eliminate the risk as effectively as avoiding the shell entirely.
- C
Avoid using shell=True and pass the command as a list of arguments
When shell=True is omitted and the command is a list, subprocess executes the command directly without invoking a shell, eliminating shell injection.
- D
Use the 'exec()' function to run the command
Why wrong: exec() is a Python built-in that executes dynamically generated Python code, not system commands, and is also dangerous.
Quick Answer
The correct choice is to avoid using shell=True and pass the command as a list of arguments. This is the most effective Python command injection mitigation because setting shell=True causes the subprocess module to hand the entire command string to the system shell for parsing, which allows shell metacharacters—like semicolons, pipes, or backticks—to be interpreted and exploited if any part of the string is user-controlled. By passing the command as a list, such as ['ls', '-l', filename], the subprocess module directly executes the binary without invoking a shell, eliminating the shell interpretation that is the root cause of the vulnerability. On the CompTIA PenTest+ PT0-002 exam, this concept tests your understanding of secure coding practices and common exploitation vectors; a frequent trap is assuming that input sanitization alone is sufficient when the real fix is removing shell=True entirely. Remember the mnemonic: "No shell, no spell"—without the shell, there is no shell metacharacter magic to exploit.
PT0-002 Tools and Code Analysis Practice Question
This PT0-002 practice question tests your understanding of tools and code analysis. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A penetration tester is reviewing a Python script that attempts to exploit a command injection vulnerability. The script uses the 'subprocess' module with the 'shell=True' argument. Which of the following code changes would be MOST effective to reduce the risk of unintended consequences when executing system commands?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Avoid using shell=True and pass the command as a list of arguments
Option C is correct because setting `shell=True` in Python's `subprocess` module causes the command string to be interpreted by the system shell, which introduces command injection risks if any part of the string is user-controlled. By passing the command as a list of arguments (e.g., `['ls', '-l', filename]`) and omitting `shell=True`, the subprocess module directly executes the binary without shell interpretation, eliminating shell metacharacter injection. This is the most effective mitigation as it avoids shell parsing entirely, which is the root cause of the vulnerability.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Replace subprocess with os.system()
Why it's wrong here
os.system() also uses a shell and is even less secure than subprocess with shell=True.
- ✗
Use the 'shlex.quote()' function to sanitize user input before passing to subprocess
Why it's wrong here
While sanitization helps, it is still prone to bypasses and does not eliminate the risk as effectively as avoiding the shell entirely.
- ✓
Avoid using shell=True and pass the command as a list of arguments
Why this is correct
When shell=True is omitted and the command is a list, subprocess executes the command directly without invoking a shell, eliminating shell injection.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use the 'exec()' function to run the command
Why it's wrong here
exec() is a Python built-in that executes dynamically generated Python code, not system commands, and is also dangerous.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that input sanitization (like quoting) is sufficient to prevent command injection, when in fact the most secure approach is to avoid shell invocation altogether by using a list of arguments with `shell=False`.
Trap categories for this question
Command / output trap
exec() is a Python built-in that executes dynamically generated Python code, not system commands, and is also dangerous.
Detailed technical explanation
How to think about this question
When `shell=True` is used, Python's `subprocess` internally calls `/bin/sh -c <command>`, which parses the string for shell metacharacters like `;`, `|`, `$()`, and backticks. By passing a list of arguments with `shell=False` (the default), the `execve()` syscall is used directly, bypassing the shell entirely and treating each list element as a separate argument to the executable—this prevents any shell injection even if an argument contains malicious characters. In real-world scenarios, this distinction is critical when handling filenames or user-supplied data that may contain spaces, quotes, or special characters, as seen in CVEs like CVE-2019-10149 (Exim) where shell injection via crafted email addresses led to remote code execution.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PT0-002 question test?
Tools and Code Analysis — This question tests Tools and Code Analysis — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Avoid using shell=True and pass the command as a list of arguments — Option C is correct because setting `shell=True` in Python's `subprocess` module causes the command string to be interpreted by the system shell, which introduces command injection risks if any part of the string is user-controlled. By passing the command as a list of arguments (e.g., `['ls', '-l', filename]`) and omitting `shell=True`, the subprocess module directly executes the binary without shell interpretation, eliminating shell metacharacter injection. This is the most effective mitigation as it avoids shell parsing entirely, which is the root cause of the vulnerability.
What should I do if I get this PT0-002 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This PT0-002 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PT0-002 exam.
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